Difference in Pass Labs X and x.5

I have a pair of Martin Logans(Ascent I ), and I am looking at used Pass amps. I would like to know if anyone had tried both series and could give any information on the sonic difference in the two. Thank you.
Mlrf18, I have had Pass Labs Alephs, X-series, X.5 series, and now XA amps in my home rig. I have written reviews of both the 350.5 and XA-100's here on the GON that should provide the detailed information that you are seeking regarding these amps sonics.

So, I won't go into details, there in the reviews, but the .5 series was a dramatic improvement over the first generation X-series amps. A match made in heaven would be your speakers with the 350.5 amp, in my opinion, and their some for sell right now, at very good prices, that are used or demo models.
Thanks for the response, I read your review and it was very informative. I do however have a budget and it look s to be about $5000 for amp and pre-amp( looking at Pass X 2.5) so I may have to go with the 250.5. The system it will replace is a Parasound P-3 pre amp and Bryston 4B-St amp. The bryston is rated at 250 wpc and is plenty loud in my room 17x20x9. If you have had any experience with the Pass pre-amps please let me know. Thanks again for your help.